(1. 上海大学 材料基因组工程研究院，上海 200444；
2. 上海大学 材料科学与工程学院，上海 200444；
3. 上海大学 省部共建高品质特殊钢冶金与制备国家重点实验室，上海 200444)
摘 要: 以纯镁为细化对象，研究Al-2.8Nb-0.3B(中间合金)作为晶粒细化剂对铸态纯镁微观组织、拉伸变形及断裂行为的影响。结果表明：随着中间合金的添加量由0增加至7.14%，晶粒由毫米级的柱状晶细化至平均直径约196 μm的等轴晶，最大拉伸应力由53.8 MPa提升至185.4 MPa，滑移线的平均间距由17.9 μm减至1.3 μm。纯镁经7.14%中间合金细化后的拉伸断裂过程与细化前的存在显著区别：细化前，晶粒内部首先产生滑移线，随后裂纹在最深的滑移台阶处萌生、扩展，并最终断裂；细化后，晶粒内部同样先产生滑移线，但随后裂纹沿晶界处的第二相β-Mg17Al12萌生裂纹和扩展，直至最终断裂。纯镁经7.14%中间合金细化后，合金发生显著的细晶强化，但细化后合金晶界处形成数十微米的β-Mg17Al12相，降低了合金的延展性。
关键字: 纯镁；Al-Nb-B细化剂；微观组织；原位拉伸；断裂机理
（1. Materials Genome Institute, Shanghai University, Shanghai 200444, China;
2. School of Materials Science and Engineering, Shanghai University, Shanghai 200444, China;
3. State Key Laboratory of Advanced Special Steel, Shanghai University, Shanghai 200444, China）
Abstract:Using pure magnesium as the refinement object, the effects of Al-2.8Nb-0.3B master alloy as a grain refiner on the microstructure, tensile deformation and fracture behavior of as-cast pure magnesium were studied. The results show that, when the addition of Al-2.8Nb-0.3B master alloy increases from 0 to 7.14%, the grains are refined from millimeter-lever columnar crystals to equiaxed crystals with an average diameter about 196 μm, and the maximum tensile stresses increase from 53.8 MPa to 185.4 MPa, and the average spaces of adjacent sliding lines reduce from 17.9 μm to 1.3 μm. The tensile fracture behaviors are evidently different before and after the refinement with Al-2.8Nb-0.3B master alloy of 7.14%. Before refinement, the slip lines first appear inside grains, followed by the nucleation and propagation of a crack along the deepest slip step, and then, the crack rapidly leads to fracture. After refinement, the slip lines also appear inside grains first, but then, a crack nucleates and propagates at the second phase β-Mg17Al12, which is mostly located at the grain boundaries. The pure Mg is refined by 7.14% master alloy remarkably, the β-Mg17Al12 second phase with size of roughly tens of microns forms at grain boundry of refined alloy, and the ductility of refined ingot decrease.
Key words: pure Mg; Al-Nb-B grain refiner; microstructure; in-situ tensile; fracture mechanism
